BACK TO BASICS: Transverse and Longitudinal Joint Construction and Compaction Thomas Travers, Director of Technical Sales, Astec Industries Charlie Butler, Customer Service Specialist, Hills Paving Equipment Division, Hills Machinery Every paving project consists of two joints—the transverse joint and the longitudinal joint. Only two transverse joints should be formed during a typical day’s paving. How well those joints are constructed and compacted will determine if the driver of a vehicle even notices they exist. Likewise, the project will consist of two longitudinal joints or a longitudinal joint with an outside edge. Since these joints run the length of the project and not a paver width (i.e., transverse), how well they are constructed and compacted greatly impacts the performance of the pavement. The following article will discuss best practices in asphalt paving construction and compaction for both transverse and longitudinal joint construction and compaction. Transverse Joint Construction and Compaction Crews are graded on three areas when constructing a transverse joint: flatness, smoothness, and density. Each is important for both the driver’s experience and the long-term quality of the road. Take a transverse joint at a bridge, for instance. If the joint is constructed poorly, then it could create a launch point with an impact that the driver feels every time they cross the bridge, and the pavement or bridge is impacted every time the tires leave and reconnect with the surface. The effect of such a long-term beating is the wearing of the asphalt or bridge, which can lead to premature failure. Everything in the lifecycle is affected by that load, so the flatter, smoother, and denser the surface, the longer the life of the asphalt and whatever is adjacent. Best Practices First and foremost, a 90-degree or vertical face (i.e., butt joint) is essential at the beginning and end, resulting in a square transverse joint. Saw cutting is usually the best way to achieve this, preferably with new, sharp blades. No worn-out or jagged edges on the blades- it will make an ugly joint and wear out your employees. Next, with wood, steel, or other materials, block the screed off the surface at the start of each lift to allow for the compacting effort of the new mat. The rule of thumb is one-quarter inch per one inch of compacted lift thickness. So, to match a compacted two-inch lift, you’d want to start your screed on top of a half-inch block to give you an uncompacted two-and-a-half-inch mat. Aligning the screed with the joint is critical. You don’t want to overhang or try to perfectly align the face of the screed with the transverse joint, which will require you to shovel material back to the joint to fill it. It’s better to stay short of the joint with the screed and remove some material from the existing pavement versus returning material to it by hand. As a rule, the less hand work (shoveling in material or raking off material), the better. Eliminating the chance for launch points or dips that create longterm problems comes down to the screed’s angle of attack coming off the joint. You want to come off right at the plane of the previous mat. The best way to do this is to use automation with a 30-footlong mat reference ski. There will always be handwork around the joint after it’s created. A straight edge of ten feet or so will do the job and is required in VDOT and many other transportation agencies’ specifications. Span it across the previous day’s compacted mat (or existing pavement for a new construction joint), slide out eight feet on the new lift (pre-compaction), and judge if any deviations will lead to a dip or a launch point. If deviations are noted, add or remove material accordingly to achieve a more consistent plane. To come off smoothly, you need a consistent head of material in front of the screed. If there’s too much material, you’ll climb, and if there’s too little, you’ll drop—avoid the bump and dip. Screed temperature is important at the start. If the screed is cooler than the asphalt material, the operator will have a drop because the material is more likely to be slow coming under the screed, which may lead to marks in the mat. If the screed is the same temperature or hotter, it will disperse the material smoothly and come off the joint true. Compaction concepts on transverse joints are fairly simple: if space allows, parallel compaction to the joint with no vibration and minimal overhang on the adjacent mat is preferred. If space does not allow, the joint should be attacked at varying angles from the previous day’s mat, slowly, and with no vibration. Longitudinal Joint Construction and Compaction Like transverse joint construction, best practices can help deliver an excellent ride for the traveling public and a low- to no-maintenance joint that will result in a longer life cycle for the pavement itself. Here are things to keep in mind. Best Practices To ensure a matching lift to an adjacent compacted mat, the matching joint should be one-quarter inch higher for every inch of the lift it matches up against. Like pulling off a transverse joint, if the final compacted lift thickness is two inches, the uncompacted mat at the longitudinal joint should be ½ inch higher. Densities on confined joints are better because the adjacent mat holds the material and creates a stronger joint. On the unconfined or open edge of a longitudinal joint, the initial restriction of an existing lane or shoulder does not exist. To create the confinement, the end gate on the screed should contact the underlying surface so that the asphalt mix gains initial compaction. If the end gate is up, asphalt material will flow under the end gate, creating a ragged joint with very little initial density and numerous 22 SPRING/SUMMER 2024
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